The present invention relates to an inlet casing or a suction passage structure which is used for suction of fluid into fluid machinery for boosting up the pressure of fluid through the rotation of an impeller mounted on a rotary shaft, and also to a fluid machinery including a pump, a compressor, a blower or the like, using thereof. In a large-sized suction passage structure, an inlet casing produced as a coupling component for the fluid machinery and used for sucking fluid into a fluid machinery is in general connected to a suction passage which is a concrete construction or the like. The above-mentioned suction passage structure includes a non prewhirl type one in which fluid is led in a form of a suction stream into an inlet opening of fluid machinery, in parallel with a first reference line passing through the center line of a rotary shaft of the fluid machine and extending along the stream of fluid directed to the fluid machine in the suction passage, and a prewhirl type one in which a swirl flow is creased by a swirl portion incorporated in an inlet casing, being orthogonal to a rotary shaft of fluid machinery or which creates a swirl flow swirling around the rotary shaft or an extension or the rotary shaft.
Referring to FIG. 6 which shows a typical nonprewhirl type suction passage structure of a conventional configuration, the suction passage structure includes a suction passage 102 arranged orthogonal to a rotary shaft of fluid machinery on the upstream side as viewed in a stream toward the fluid machinery, and an internal passage 104 in a suction casing 103, which are arranged, being symmetric with each other to a first reference line C1 (which passes through the center line of a rotary shaft 101 while it also passes through a heightwise center position of the suction passage 102 or the internal passage 104, and which extends along a stream of fluid toward the fluid machinery in the suction passage 102 and the internal passage 104, a second reference line C2 being orthogonal to the first reference line C1). That is, the suction passage 102 and the internal passage 104 are arranged so that their center lines are substantially superposed on the first reference line C1. Thus, the fluid flowing in parallel with the reference line C1 in the suction passage 102 still flows in parallel with the first reference line C1 in the internal passage 104 even after passing through an inlet opening 105 of the inlet casing 103 which is a connection between the suction passage 102 and the inlet casing 103, and comes to a suction opening through which the fluid is sucked into an impeller 106 mounted on the rotary shaft 101.
Thus, the fluid led into the suction passage structure of the nonprewhirl type flows into the suction opening of the impeller on both sides of the reference line C1 while it interferes with a baffle portion 107 incorporating the most downstream part of the internal passage 104, and accordingly, there would be presented a zone where an inflow angle of the fluid at the inlet opening of the impeller and the angle of the inlet opening thereof are different from each other. As a result, there have been raised such disadvantages that a zone where cavitations are caused would be deviated, and further, serious vibration and noise would be possibly caused.
Referring to FIG. 7 which shows a conventional typical configuration of a prewhirl type, a suction passage structure of this type, includes a swirl part 113 which is provided in an internal passage 112 of an inlet casing 111, which is formed in a spiral shape and with which a swirl stream of fluid is induced, orthogonal to a rotary shaft 101. Thus, the fluid is sucked into a suction opening of an impeller 106, flowing in one way direction, while it interferes with a baffle portion 114 provided in the most upstream part of the swirl part 113.
The above-mentioned prewhirl type suction passage structure can avoid occurrence of the problem of deviation of a cavitations inducing zone which inherent to the conventional nonprewhirl type one. However, the prewhirl type suction passage structure has raised such a problem that the suction passage and the internal passage can hardly be formed, symmetric to each other with respect to the first reference line C1 as in the nonprewhirl type one. That is, as exhibited in an example shown in FIG. 8, should the suction passage 102 and the internal passage 116 of the inlet casing 115 be symmetric to each other, fluid guided through the suction passage 102 and the internal passage 116 would flow into the suction opening of the impeller 106 without being subjected to any resistance, and accordingly, it would induce both stream A which is steeply curved in a direction along the rotary shaft 101 and stream B which crosses the rotary shaft 101. The stream A is likely to peel off at the suction opening 117 of the impeller 106 while the stream B causes a wake at the rear surface part of the rotary shaft 101 so that a secondary stream occurs, resulting in deterioration of uniformity of the stream at the suction opening 117.
Thus, the conventional prewhirl type suction passage structure in general has in general such a structure, as shown in FIG. 7, that the suction passage 102 and the internal passage 112 are formed so as to be asymmetric with each other with respect to the first reference line C1, that is, they are eccentric with each other, in order to obtain uniformity of a stream at the suction opening of the impeller 106. In such an asymmetric configuration, it is required to provide a connection 106 between the suction passage 102 and the internal passage 112 in relatively upstream side part, resulting in occurrence of such a problem that the inlet casing 111 inevitably has a large size. Further, the spiral shape of the swirl part 113 of the internal passage 112 has to have a complicated curve. As a result, there has been raised such a problem that the design and fabrication thereof becomes complicated, resulting in an increase the costs thereof.
Further, in the prewhirl type suction passage structure, in order to constrain occurrence of both stream A and stream B shown in FIG. 8 so as to enhance the uniformity of the stream, there has been known such a configuration that an element which serves as a resistance against a stream of fluid in the internal passage 112 is provided in the downstream part of the internal passage 112. For example, as such an element, JP-A-51-142101 discloses a protrusion, and JP-A-11-148498 discloses a bevel shape bulge. However, it has not been sufficient with these elements to always main required uniformity of the stream, and accordingly, the suction passage and the internal passage are inevitably formed, symmetric to each other as in the example shown in FIG. 7.
The nonprewhirl type suction passage structure and the prewhirl type suction passage structure have been known as disclosed in JP-A-63-44960 in addition to the above-mentioned JP-A-51-142101 and JP-A-11-148498.
As stated above, there are used both nonprewhirl type suction passage structure and prewhirl type suction passage structure for fluid machinery. The nonprewhirl type suction passage structure may have the suction passage and the internal passage which are symmetric with each other, and accordingly, there may be offered such an advantage the shape of the internal passage can be simple so that it can be easily designed and fabricated but also offered such a disadvantage that a deviation of the cavitations inducing zone likely to occur. Meanwhile, the prewhirl type suction passage structure may avoid occurrence the problem of a deviation of the cavitations inducing zone, but the configuration of the internal passage becomes complicated so as to raise such a problem that the costs thereof is increased in view of its design and fabrication.